Detailed Explanation:

Graphite and diamond are allotropes of carbon—different physical forms of the same element. Both consist of pure carbon atoms and thus undergo identical chemical reactions (e.g., combustion in oxygen to form CO₂).

They differ drastically in crystal structure (graphite: hexagonal layers; diamond: tetrahedral lattice), hardness (graphite: soft; diamond: hardest natural material), and electrical conductivity (graphite: conducts; diamond: insulator)—eliminating Options 1, 2, and 3.

Therefore, only their chemical reactivity is identical, making Option 4 the correct answer.